1. Field of the Invention
The present invention relates to a selectably elevatable coiled tubing injector for a mobile self-contained unitized coil tubing rig for the drilling and workover of petroleum wells. In particular, the present invention concerns a mechanism for positioning a trailer mounted coiled tubing injector either in a first stowed position on the deck of the transport trailer or in a second position resting on an elevated rig floor of a drilling rig.
2. Description of the Related Art
Coiled tubing rigs primarily include a tubing storage reel and a coiled tubing injector for forcing a string of coiled tubing into or pulling it out of a well. Coiled tubing rigs are commonly used in the oilfield for reasons of speed and low cost operation. Due to advances in the ability to run downhole drilling motors on the lower end of a coiled tubing drill string, a need has arisen for coiled tubing injectors which can be positioned on a rig floor so that the tubing from the injector is coaxially aligned with the well bore. Previously, this need has been filled by lifting a self-contained conventional injector from a transport trailer to the rig floor using large forklift trucks, cranes, or other means. Upon completion of a job by such an injector, the injector has to be lifted back onto the transport trailer.
When being transported, such a conventional injector must be restrained by tiedown means, so the conventional approach involves considerable setup and rig down time, as well as necessitating lifting equipment. Additionally, the storage reel must be carefully positioned during the lifting to and from the rig floor in order to avoid damaging the tubing, particularly when the tubing is left engaged with the injector. If the tubing is released from the injector for lifting, then it must be rethreaded through the injector after the injector has been lifted.
Accordingly, a need exists for a coiled tubing injector which can be moved more readily between a transport trailer and a rig floor.
Furthermore, whenever a coiled tubing string is used to drill wells with a downhole motor, the tubing often becomes stuck in the hole due to pressure differentials between the hole and adjacent formations. Whenever this happens, it is necessary to exert considerable upward force on the tubing to free it from the well. Likewise, to retrieve packers from a well and for a variety of other downhole operations, large vertical pulls are needed. These vertical uplift forces are often in excess of what can be provided by the drive means of conventional coiled tubing injectors.
Thus, there is a need for a mechanism that can easily provide additional tension to a coiled tubing string beyond that which can be provided by a conventional coiled tubing injector.